code: def ckpt_at_epoch(num):
      return "%s_%s" % (num, constants.CKPT_NAME)
  
imports: import torch
  import shutil
  import dill
  import os
  from subprocess import Popen, PIPE
  import pandas
  from PIL import Image
  from .None import constants
label_desc: Use image node_id 3 for calling a global function with example usage: ckpt_at_epoch(num) and returns: unknown